Imaging based calibration systems, devices, and methods

ABSTRACT

Systems, devices, and methods for imaging-based calibration of radiation treatment couch position compensations.

FIELD

The present disclosure relates generally to radiation therapy systems,devices, and methods, and more particularly to imaging-based calibrationsystems, devices, and methods for accurate target positioning andlocalization.

BACKGROUND

In radiosurgery or radiotherapy (collectively referred to as radiationtreatment) very intense and precisely collimated doses of radiation aredelivered to the target region in the body of a patient in order totreat or destroy lesions. Typically, the target region is comprised of avolume of tumorous tissue. Radiation treatment requires an accuratespatial localization of the targeted lesions. Stereotactic radiosurgery(SRS) is a specific type of image-based treatment, which delivers a highdose of radiation during a single session. Because a single radiosurgerydose is more damaging than multiple fractionated doses, the target areamust be precisely located.

In general, radiation treatments consist of several phases. First, aprecise three-dimensional (3D) map of the anatomical structures in thearea of interest (head, body, etc.) is constructed using any one of (orcombinations thereof) a computed tomography (CT), cone-beam computedtomography (CBCT), magnetic resonance imaging (MRI), positron emissiontomography (PET), 3D rotational angiography (3DRA), or ultrasoundtechniques. This determines the exact coordinates of the target withinthe anatomical structure, namely, locates the tumor or abnormalitywithin the body and defines its exact shape and size. Second, a motionpath for the radiation beam is computed to deliver a dose distributionthat the surgeon finds acceptable, taking into account a variety ofmedical constraints. During this phase, a team of specialists develop atreatment plan using special computer software to optimally irradiatethe tumor and minimize dose to the surrounding normal tissue bydesigning beams of radiation to converge on the target area fromdifferent angles and planes. Third, the radiation treatment plan isexecuted. During this phase, the radiation dose is delivered to thepatient according to the prescribed treatment plan.

The objective of radiation therapy is to accomplish tumor control whilesparing the normal tissue from radiation induced complications. This,however, requires an exact knowledge of the target position (tumorposition) not only at the planning stage but also the actual treatmenttimes. Conventionally, the tumor position is determined at one singletime during the treatment planning. This information may not, however,be accurate during treatment delivery due to patient setup errors, organmotion, and variations of the geometric parameters of the system.

The prevalence of target-conforming beams, as well as the movementtoward hypofractionation and dynamic arc IMRT, increases the need foraccurate target positioning. Image guidance provides an improvement inpositioning accuracy. Image guidance involves acquiring setup images,such as kV radiographs and/or MV portal images from multiple gantryangles, or room based X-ray systems, or MV and/or kV Cone Beam CT, aswell as in-room spiral CT's or MRI images to help target localization.If gantry and imager rotation about the isocenter would be completelyrigid and planar, the target positions determined from images frommultiple angles would be accurate. However, gantry and imager rotationabout the isocenter is not rigid and planar. Instead, a gantry head sagimposed by the weight of the gantry head, as well as similar sags in thesupports for the MV image panel, kV image panel, and kV sourcecontribute to displacements of the imaging axis and the radiation beamaxis from the isocenter. Therefore, a target position determined fromimages obtained at multiple gantry angles could be offset significantly.In order to compensate for these offsets, the deviations between thetreatment beam axis and the imaging axis need to be determined for allgantry angles and the deviations corrected.

Using a treatment couch to compensate for such deviations requires ahigh precision treatment couch, especially for high precision treatmentssuch as stereotactic radiosurgery and stereotactic body radiation.Treatment couches, however, have mechanical weaknesses which, if notcorrected, introduce errors in the accurate positioning and localizationof the target. The currently available couch compensation models thatcorrect for mechanical weaknesses, such as load dependent deflections,of the radiation treatment couches are couch dependent, and do notcorrect for installation variations or readout system productionvariations.

SUMMARY

An object of the present invention is to provide imaging-based systemsand methods for couch offset compensations which are capable of removinginstallation specific imperfections.

Another object of the present invention is to provide imaging-basedsystems and methods for positioning a treatment couch precisely to theradiation beam isocenter for all combinations of couch rotations andgantry positions.

Another object of the present invention is increasing the accuracy ofcouch compensation by taking into consideration not only the gantrydependent isocenter variations but also the effects of the treatmentcouch rotation relative to the isocenter.

Embodiments of the present disclosure provide imaging-based calibrationmethods for correcting target positions by combining gantry angledependent target position information with couch rotation angledependent couch position offset information.

Embodiments of the present disclosure further provide methods forgenerating gantry angle dependent target position information fordifferent gantry angles, and generating couch rotation angle dependentcouch position offset information for different couch rotation angles.

Embodiments of the present disclosure further provide methods forcorrecting target positions at different gantry angles and differentcouch positions by combining gantry angle dependent target positioninformation with couch rotation angle dependent couch position offsetinformation.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments will hereinafter be described with reference to theaccompanying drawings, which have not necessarily been drawn to scale.Where applicable, some features may not be illustrated to assist in theillustration and description of underlying features.

FIG. 1 illustrates a radiation treatment system according to one or moreembodiments of the disclosed subject matter.

FIG. 2 illustrates a process flow according to one or more embodimentsof the disclosed subject matter.

FIG. 3 illustrates a flow diagram of an imaging-based calibrationprocess according to one or more embodiments of the disclosed subjectmatter.

FIG. 4 illustrates an imaging-based calibration process according to oneor more embodiments of the disclosed subject matter.

FIG. 5 illustrates an imaging-based automatic target positioning methodaccording to one or more embodiments of the disclosed subject matter.

DETAILED DESCRIPTION

Patients undergoing radiation therapy are typically placed on atreatment platform of a radiation treatment gantry. The gantry has aradiation source that is used to generate a radiation beam thatirradiates a region of interest in the patient, such as a diseased issueincluding a tumor or cancerous growth site. When delivering theradiation, a plurality of radiation beams may be directed to the targetarea of interest from several positions outside the body. The gantry canbe rotated to provide the radiation beams from different positions. Thepoint at which beam trajectories converge or intersect is generallyreferred to as the isocenter. The isocenter typically receives thelargest radiation dose because of the cumulative radiation received frommultiple radiation beams. An integral part of the radiation treatmentprocess is the accurate positioning of the target volume/patient at theisocenter throughout the radiation treatment process. Setup images, suchas kV radiographs, and/or MV portal images, or room-based X-ray systemimages, or MV or kV Cone Beam CT, as well as in-room spiral CTs or MRIimages, can be acquired from multiple gantry angles to aid in theaccurate positioning of the patient. Because of the hardware flex, thehead sag imposed by the weight of the gantry head, as well as sags inthe supports for the MV image panel, kV image panel, and kV source, atarget position determined from images from multiple angles may beoffset significantly. Therefore, an integral part of the radiationtreatment process is dependent upon the calibration of the treatmentbeam axis and the imaging axis for all gantry angles. In the prior artsystems and methods, when an offset is determined between the treatmentbeam and the imaging beam, the imaging systems (on a Truebeam system,for example) or the acquired images (on Clinacs and Trilogies systems,for example) are shifted to the isocenter instead of moving thetreatment couch to correct for the offset.

In the disclosed embodiments, however, when a positioning offset isdetermined between the reference images of the target region (e.g.,volume to be treated, tumor) and the images acquired during theradiation treatment session for each gantry angle, the offset can becorrected by an operator initiated automatic couch shift from thetreatment console room. Thus, the offsets can be automaticallytransferred to treatment couch motion from the treatment console.

Using a treatment couch to compensate for these offsets requires a highprecision treatment couch, especially for high precision treatments suchas stereotactic radiosurgery and stereotactic body radiation. Treatmentcouches have a high precision readout system built into them so as toallow for small couch shifts with high accuracy. The latest generationof couches (used on the Varian Truebeam Systems, for example) alsoinclude in their readout system, software to compensate for thestructural deflection of these couches caused by the elastic mechanicaldistortions of the supporting structure and internal components, whichposition deviations are not otherwise being measured by the couchreadout system. These position deviations are induced by gravity loadson the couch such as the weight of the patient and its relatedpositioning aids (breast boards, arm rests and the like). The resultingdeviations are load, as well as axis position dependent. They are alsodepending on the construction of the couch, but not on the individualcouch, or the expected manufacturing variations. These structuraldeflection compensation models are used for correcting the constructiondependent deviations of the couch, either for a typical load (forexample between 65 to 95 kg), or, for even higher accuracy, for on theactual load, which can be measured by the couch, measured externally, orinputted as a patient specific treatment parameter.

The currently available readout systems and compensation models are,however, not compensating for errors due to different installationvariations, different couch dynamics, and readout system productionvariations. Therefore, another integral part of the radiation treatmentprocess is the accurate couch positioning over large ranges, which inturn is dependent on the accurate determination of the couch offsetvalues for all couch rotation angles.

An exemplary radiation treatment system 100 that integrates radiationtreatment delivery and patient setup verification is illustrated inFIG. 1. The treatment system 100 can provide radiation therapy to apatient 110 positioned on a treatment couch 102, as well as isocentercoincidence verification and couch motion offset determination prior tothe commencement of the radiation treatment. The radiation therapytreatment can include photon-based radiation therapy, particle therapy,electron beam therapy, or any other type of treatment therapy.

In an embodiment, the radiation therapy treatment system 100 includes aradiation treatment device 116, such as, but not limited to, aradiotherapy or radiosurgery device, which has a gantry 112 supporting aradiation module 114 with one or more radiation sources 106 and a linearaccelerator (LINAC) 104 operable to generate a beam of kilovolt (kV) ormegavolt (MV) X-ray radiation. The gantry 112 can be a ring gantry(i.e., it extends through a full 360° arc to create a complete ring orcircle), but other types of mounting arrangements may also be employed.For example, a static beam, or a C-type, partial ring gantry, or roboticarm can be used. Any other framework capable of positioning theradiation module 114 at various rotational and/or axial positionsrelative to the patient 110 may also be used.

The radiation module 114 can also include a modulation device (notshown) operable to modulate the radiation beam as well as to direct thetherapeutic radiation beam toward the patient 110 and a portion thereofthat is to be irradiated. The portion desired to be irradiated isreferred to as the target or target region or a region of interest. Thepatient 110 may have one or more regions of interest that need to beirradiated. A collimation device such as a conventional 4 jaw collimatora multileaf collimator or fixed cones or applicators (not shown) may beincluded in the modulation device to define and adjust the size of anaperture through which the radiation beam passes from source 106 topatient 110. The collimation device can be controlled by an actuator(not shown), which can be controlled by controller 120.

In an embodiment, the radiation therapy device is a MV energy intensitymodulated radiotherapy (IMRT) device. The intensity profiles in such asystem are tailored to the treatment requirements of the individualpatient. The IMRT fields are delivered with a multi-leaf collimator(MLC), which can be a computer-controlled mechanical beam shaping deviceattached to the head of the LINAC 104 and includes an assembly of metalfingers or leafs. The MLC can be made of 120 movable leafs with 0.5 cmand/or 1.0 cm leaf width, for example. For each beam direction, theoptimized intensity profile is realized by sequential delivery ofvarious subfields with optimized shapes and weights. From one subfieldto the next, the leafs may move with the radiation beam on (i.e.,dynamic multi-leaf collimation (DMLC)) or with the radiation beam off(i.e., segmented multi-leaf collimation (SMLC)). The device 116 can alsobe a tomotherapy device where intensity modulation is achieved with abinary collimator which opens and closes under computer control. As thegantry 112 continuously rotates around the patient 110, the exposuretime of a small width of the beam can be adjusted with opening andclosing of the binary collimator, allowing radiation to be delivered tothe tumor through the most desirable directions and locations of thepatient.

Alternatively, the device 116 can be a helical tomotherapy device, whichincludes a slip-ring rotating gantry or an intensity modulated arctherapy device (IMAT), which uses rotational cone beams of varyingshapes to achieve intensity modulation instead of rotating fan beams.Indeed, any type of IMRT device can be employed as treatment device 116.For example, embodiments of the disclosed subject matter can be appliedto image-guided radiation therapy (IGRT) devices. Each type of device116 can be accompanied by a corresponding radiation plan and radiationdelivery procedure.

The treatment couch 102 is positioned adjacent to the gantry 112 toplace the patient 110 and the target volume within the range ofoperation of the X-ray source 106. The treatment couch 102 may beconnected to the rotatable gantry 112 via a communications network andis capable of translating in multiple planes and angulations forpositioning and repositioning the patient 110 and the target volume. Thetreatment couch 102 can have three or more degrees of freedom. Thetreatment couch 102 can be coupled to an automated patient positioningsystem capable of manipulating the patient with three or more degrees offreedom (e.g., three orthogonal translations plus one or morerotations). In embodiments, the treatment couch 102 can have six (6)degrees of freedom (i.e., 6 DoF couch), namely, it can move in thevertical, lateral, longitudinal, rotation (yaw), roll, and pitchdirections (x, y, z, θ₁, θ₂, θ₃). In such a case, the automated patientpositioning system is capable of manipulating the patient with sixdegrees of freedom (e.g., three orthogonal translations and threerotations). In other embodiments, the treatment couch 102 can have four(4) degrees of freedom (i.e., 4 DoF couch), namely, it can move in thevertical, lateral, longitudinal directions and have one rotationdirection (x, y, z, θ₁). In such a case, the automated patientpositioning system is capable of manipulating the patient with fourdegrees of freedom (e.g., three orthogonal translations and onerotation).

The treatment couch 102 includes a built-in high precision readoutsystem to allow for small couch shifts with high accuracy. The readoutsystem can be a digital readout system and can include one or more couchangle encoding potentiometers, or other position and angle sensors,including, but not limited to, optical or magnetic rotary (angle) orlinear encoders. These position and angle sensors and potentiometers,supply input signals regarding the positions/movement/angle of thetreatment couch 102 to the digital readout system on the console. Theencoders include serial interface technology to provide secure datatransmission of absolute positioning values. The encoders can be fittedwith the treatment couch 102 and can be integrated with the radiationtreatment system. For example, one or more encoders can be used in themotor packages that operate in conjunction with the couch'svertical/downwards/lateral movement. Additional encoders are used forthe pitch and roll motion axis of the treatment couch 102. Each axis ofmovement can also have secondary, ‘fail-safe’ encoders, which duringsystem operation constantly check against the primary ‘master’ encodersfor successful non-stop system operation.

The readout system also includes software that integrates treatmentcouch travel and positioning with beam delivery, as well as software tocompensate for the structural deflection of the couch 102 caused by theelastic mechanical distortions of the supporting structure and internalcomponents, which position deviations are not otherwise being measuredby the couch readout system. These position deviations are induced bygravity loads on the couch such as the weight of the patient and itsrelated positioning aids (breast boards, arm rests and the like). Theresulting deviations are load, as well as axis position dependent. Theyare also dependent on the construction of the couch 102 and the expectedcouch manufacturing variations. These structural deflection compensationmodels are used for correcting the construction dependent deviations ofthe couch, either for a typical load (for example between 65 to 95 kg),or, for even higher accuracy, for the actual load, which can be measuredby a measuring device integrated with the couch 102, measuredexternally, or inputted as a patient specific treatment parameter. Thetreatment couch 102 can be positioned along a vertical axis at a heightwhich is at one of the height of the isocenter, above the isocenter, orbelow the isocenter.

Device 116 can also include a holding structure 118, which could be arobotic, servo controlled arm holding an imager 108 for acquiringdigital images. The imager 108 can include a megavoltage (MV) electronicportal imaging device (EPID). The imaging device 108 can be placed atdifferent locations, and can generate immediate 2-D digital information.By acquiring a plurality of MV images at different gantry angles, aMV-Cone beam CT image can be generated and be used for positioning.

The system 100 can further include a (kV) X-ray imaging system includingan X-ray source 122 and a corresponding X-ray detector/imager 124, bothinstalled on the gantry 112 using arms 123, 125 to allow for patientsetup and target localization. The kV imaging system not only allows 2Dpatient setup, but it can also acquire cone beam CT (CBCT) for 3Dpatient setup. In general, this is done by generating a plurality of kVimages using the kV imaging system right before the start of eachradiation treatment session and comparing the acquired images withcorresponding patient reference images previously generated during thetreatment planning phase. The detected differences between the onlineimages (either 2D-kV image or 3D-CBCT image) and the patient referenceimages (either 2D-DRR images or 3D-planning CT images) can beautomatically transferred to treatment couch motion from the treatmentconsole including controller 120, as described in detail herein.

Arms 123, 125 could be electronically stabilized, robotic arms(electronic servo arms, for example) that hold the X-ray source 122 andthe imager 124 in a stable configuration relative to the gantry 112. Thearms 123 and 125 can have parked, partially extended, and extendedpositions. These positions can be programmed into the controller 120,and the arm positions can be extended or retracted remotely. Each of thearms 123, 125 can be controlled individually, as a pair, or togetherwith arm 118.

The kV X-ray imaging system can be mounted on the gantry 112 orthogonalto the MV X-ray imaging system 108, while sharing the same isocenter ofthe radiation treatment source 106. The X-ray source 122 could be anX-ray tube, and the X-ray detector/imager 124 could be ahigh-performance flat-panel imager, for example. Both the X-ray source122 and the X-ray imager 124 could be moved laterally and longitudinallyrelative to the treatment beam, and be rotated through 360 degreesaround the patient together with the X-ray radiation treatment source106 and MV X-ray imager 108 in both clockwise and counterclockwisedirections. The movement of the X-ray source 122 and X-ray imager 124could also be controlled by the controller 120.

Controller 120 can include a computer with typical hardware such as aprocessor, and an operating system for running various software programsand/or communication applications. The computer can include softwareprograms that operate to communicate with the radiation therapy device116, which software programs are operable to receive data from externalsoftware programs and hardware. The computer can also include anysuitable input/output devices adapted to be accessed by medicalpersonnel, as well as input/output (I/O) interfaces, storage devices,memory, keyboard, mouse, monitor, printers, scanner, etc. The computercan also be networked with other computers and radiation therapysystems. Both the radiation therapy device 116 and the controller 120can communicate with a network as well as a database and servers. Thecontroller 120 can be configured to transfer medical image related databetween different pieces of medical equipment.

The system 100 can also include a plurality of modules containingprogrammed instructions (e.g., as part of controller 120, or as separatemodules within system 100, or integrated into other components of system100), which instructions cause system 100 to perform different functionsrelated to radiation therapy/surgery, as discussed herein, whenexecuted. The system 100 can, for example, include a treatment deliverymodule operable to instruct the radiation therapy device 116 to delivera radiation plan with or without the patient 110 in place; an imageprocessing module operable to receive images from the kV X-ray imager124 as well as the MV X-ray imager 108; a comparison module operable tocompare the acquired kV and MV X-ray images with corresponding referenceimages and determine shifts between the kV imaging axis, the MV imagingaxis, and the radiation beam axis; an isocenter calibration moduleoperable to align the kV/MV imaging isocenters to the treatmentisocenter based on the comparison; a calculation module operable todetermine the amount of alignment needed (i.e., isocenter shift/offsetdetermination); a couch offset determination module operable todetermine couch offset information relative to the isocenter at eachcouch rotation angle; a calibration module operable to combine thegantry angle dependent isocenter offset information with the couchoffset information, generate gantry angle dependent couch offsetinformation, and generate correction information for all treatment couchaxis based on the gantry angle dependent couch offset information. Themodules can be written in C or C++ programming languages, for example.Computer program code for carrying out operations as described hereinmay also be written in other programming languages.

The system 100 including the kV imaging system 122, 124 and the MV X-rayimager 108 integrated with the radiation treatment device 116 allows allimage guidance activities, such as, image acquisition, imageregistration/interpretation, and patient correction to occur remotely.Remote couch motion allows for all axis of the treatment couch 102 to beadjusted remotely based on the information generated by the system.System 100 also allows capture of all data needed for the imageacquisition (i.e., gantry angle, reference images, imager positions,type of image to be acquired (radiograph or CBCT), etc.). All data canbe transferred between different computers and radiation therapy systemsusing DICOM RT (RT Plan, RT Structure Set, RT Image Objects) as shown inFIG. 2. Although, the illustrative embodiment includes a kV imagingsystem which is integral with the gantry 112, the kV imaging system canbe a separate imaging system, such as a room based imaging system.

FIG. 2 illustrates a clinical workflow (process) using X-ray imaging forpatient/target localization. The radiation treatment includes acquiringa treatment planning scan of a patient in the treatment position in thetreatment planning room. The combination of the resulting CT images andassociated contours defines a reference CT dataset. The reference CTdataset is imported to the workstation in the control room. The patientis then positioned on the treatment couch 102 in the treatment room.Localization imaging, such as, but not limited to, CBCT imaging, is thenperformed, using the X-ray imaging system. After scanning, thelocalization images are registered to the reference CT images todetermine the patient and tumor position. The alignment/fusion of thesetwo datasets may be performed using different algorithms. The result ofthe alignment is the determination of the required adjustments in thepatient/tumor positions. Once the required adjustments are determined,the necessary translations/rotations are automatically sent to thetreatment device and the treatment couch 102 is automatically moved. Theregistration information and the fusion graphic can be stored in adatabase.

Calibration Procedure

In operation, prior to radiation treatment of the patient 110, as partof an implemented quality assurance (QA) protocol, the controller 120initiates an imaging-based calibration process S100, shown in FIG. 3,that compensates for gantry angle dependent isocenter deviations as wellas couch motion offsets. The first step S101 in the calibration processS100 includes a process by which the MV treatment beam axis, the MVimaging axis, and the kV imaging axis are calibrated to the isocenter.This process S101 can include, but is not limited to, the automatedIsoCal™ calibration method (Varian Medical Systems, Palo Alto, Calif.),incorporated herein by reference in its entirety. The IsoCal calibrationmethod includes a combination of hardware (calibration phantom/device,collimator plate) and software to automatically align the imagingisocenters to the treatment isocenter using the calibration phantom andassociated software.

In Step S101, a calibration device, such as a calibration phantom, ofknown geometry, and a collimator or transmission plate with aradio-oblique pin are positioned on the treatment couch 102 in a securedknown fixed position. The calibration device (phantom) can be, but isnot limited to, an acrylic cube with engravings to indicate the centersof each surface to aid aligning the calibration cube at an isocenter.Inside the cube, at its center, a small (2 mm range) tungsten-carbide BBsphere can be positioned. One or more additional markers includingvisible and IR reflective markers can be positioned on different sidesand locations of the cube. These markers can be made of materials thatallow them to be distinguishable from the rest of the image. Any otheravailable calibration devices, such as, but not limited to, a 6D QAphantom, appropriate for kV imaging, MV imaging, and treatment andcoordinate coincidence verifications may be used. Other calibrationdevices, such as those appropriate for isocenter determination,positioning of the patient at the treatment device using various kindsof positioning and monitoring systems (kV, MV, CT, CCBCT, DTS, andoptical surface monitoring system), testing and validating themeasurement accuracy of two-dimensional (2D) and three-dimensional (3D)image measurement devices and tools installed on the medical imagingsystem 100, as well as verification of the measurement accuracy ofdigital image viewing stations that include diagnostic, clinical review,internet browser and teleradiology network of transferred medicaldiagnostic image systems can also be used. The calibration device(phantom) can be a three-dimensional phantom assembly that can be usedto independently verify the phantom or isocenter position by the use ofvarious positioning systems available on the treatment device, and isable to quantitatively determine the shift between the differentisocenter/imaging centers used. The calibration device is alsoconfigured to facilitate image-based positioning of the calibrationdevice using kV, MV, and optical surface monitoring.

Next, the automated isocenter calibration system and method involvesaligning the imaging isocenters (kV/MV imaging axis) to the treatmentisocenter (treatment beam axis) by imaging the calibration phantom ofknown geometry at four (4) collimator positions (the collimatorpositions can have more or less than 4 collimator positions) forexample, to find its axis, and then taking a plurality of kV X-ray andMV X-ray projection images of the calibration phantom with the kVsource/imager system 122/124, and the MV source/imager system 106/108,respectively, at a plurality of gantry angles during a 360 degreerotation of the gantry 112 around the calibration phantom. In anexemplary embodiment, the gantry 112 can be rotated at an increment of 1degrees between the acquisition of each image for a complete 360 degreerotation, for example, where at zero (0) degrees, the gantry is pointingto the floor, and at 180° it is pointing to the ceiling. The gantry 112,however, can be rotated at different increments of gantry angles. Thegantry could also be rotated for less than 360 degrees. Alternatively,the gantry 112 can be rotated at an increment of 1 degrees between theacquisition of each image for a complete 360 degree rotation, forexample, where the starting position of the gantry is at 180 degrees.The gantry 112, however, can be rotated at different increments ofgantry angles. The gantry could also be rotated for less than 360degrees.

From the plurality of kV and MV projections so obtained, an algorithm,such as, but not limited to, IsoCal™ calibration algorithm can beapplied to determine the gantry 112 rotational axis and the positions ofthe three isocenters on it (kV/MV imager isocenter and MV radiationtreatment beam isocenter). The isocenters are next projected onto theimagers 108, 125 to determine correction shift vectors. The correctionshift vectors Δ_(in) (beam isocenter offsets) are 2D vectors (x, y)which indicate the lateral and longitudinal offsets, respectively,between the treatment beam isocenter and the kV/MV image centers. Thecontroller 120 can also generate a correction file including thecorrection shift vectors Δ_(in) indicating the deviations of the actualtreatment beam at each gantry angle (θ_(gn)). These gantry-angledependent deviations (Δ_(in)) can be later applied to the MV/kV systemto correct for offsets in the positions of the imaging axis. Correctingthe offsets in the positions of the imaging axis can be done by applyingthe gantry dependent position offsets (Δ_(in)) to the imaging system(imager arm or X-ray tube arm) or by shifting the acquired images by theamount of the image system offset (Δ_(in)). Once the offsets arecorrected, the exact position of the calibration phantom in relation tothe isocenter can be determined for each gantry angle in the rangeθ_(g0)-θ_(gn), where n could be, but is not limited to, 360. By knowingthe exact position of the calibration phantom relative to the isocenterat each gantry angle, in step S102, the position of a target relative tothe isocenter can be determined for each gantry angle, and thus,gantry-angle dependent target position information (T_(n)) can begenerated. The beam isocenter offset values (Δ_(in)) together with thecorresponding gantry angles (θ_(gn)) and respective target (T_(n)), andcorresponding couch (C_(n)) locations, relative to the isocenter can berecorded in a tabular format, as a correction file, as shown in Table 1below, and saved in a memory of the controller 120, for example.

TABLE 1 Gantry Angle Θ_(g0) Θ_(g1) Θ_(g2) Θ_(g3) Θ_(g4) . . . . . .Θ_(gn) Θ_(gn) (degrees) Beam Isocenter Δ_(i0) Δ_(i1) Δ_(i2) Δ_(i3)Δ_(i4) . . . . . . Δ_(in) Offset Information Δ_(in) Target Position T₀T₁ T₂ T₃ T₄ . . . . . . T_(n) T_(n) relative to the isocenter CouchLocation C₀ C₁ C₂ C₃ C₄ . . . . . . C_(n) relative to isocenter C_(n)(x, y, z, θ₁, θ₂, θ₃)

Couch Rotation-Angle Dependent Couch Offset Calculation

In step S103, the couch rotation angle dependent couch position offsetinformation is generated. During this step, a plurality of megavoltageMV X-ray images of the calibration phantom are captured by the MV imager108 using MV X-rays from source 106, while the couch 102 is rotated overits entire couch rotation range. The couch rotation range includes 360degrees, for example. However, in alternative embodiments, the couchrotation range can include less than 360 degrees. To capture the MVX-ray images, the gantry 112 is positioned at a first position, at 0degree angle (MV source at the 12 o'clock position radiating downwards,i.e., at zero degrees the gantry is pointing to the floor, and at 180°it is pointing to the ceiling) for example, and the treatment couch 102is rotated in a clockwise direction from a first starting position toits maximum rotation angle (maximum rotation angle for the treatmentcouch could be, but is not limited to, 100 degrees), while images areacquired at 1 degree rotation angle increments. Thus, for each degree ofcouch rotation, a MV X-ray image of the calibration phantom isgenerated. Then, the treatment couch 102 is rotated to its maximumrotation angle in a second, counterclockwise direction, acquiring a MVX-ray image at each 1 degree rotation increment. In the exemplaryembodiment, the rotation of the treatment couch 102 is in 1 degreeincrements. However, the treatment couch 102 can be rotated at any otherdegree increments, such as, but not limited to, 1.5 or 2 degreeincrements.

Next, the gantry 112 is positioned in a second position, such as between5-60 degrees or between 30 and 60 degrees, (between the 1 o'clock andthe 2 o'clock positions) for example, and the treatment couch 102 isrotated to its maximum rotation angle in the clockwise direction whileacquiring MV X-ray images of the calibration phantom at a plurality ofcouch rotation angles. The treatment couch 102 can be rotated in 1degree increments, and at each couch rotation angle a correspondingX-ray image can be acquired. The treatment couch is then rotated to itsmaximum rotation angle in a counterclockwise direction while acquiringMV X-ray images of the phantom at a plurality of couch rotation angles.The treatment couch 102 again can be rotated 1 degrees at a time and acorresponding X-ray image generated. In the exemplary embodiment, therotation of the treatment couch 102 is in 1 degree increments. However,the treatment couch 102 can be rotated at any other degree increments,such as, but not limited to, 1.5 or 2 degree increments.

Next, the gantry 112 is positioned in a third position, such as between300 and 355 or between 320-340 degrees (between the 10 o'clock and the11 o'clock positions), for example, and the treatment couch 102 isrotated to its maximum rotation angle in the clockwise direction whileacquiring MV X-ray images of the calibration phantom at a plurality ofcouch rotation angles. The treatment couch 102 can be rotated in 1degree increments, and at each couch rotation angle a correspondingX-ray image can be acquired. The treatment couch is then rotated to itsmaximum rotation angle in a counterclockwise direction while acquiringMV X-ray images of the calibration phantom at a plurality of couchrotation angles. The treatment couch 102 again can be rotated 1 degreeat a time and a corresponding X-ray image generated. In the exemplaryembodiment, the rotation of the treatment couch 102 is in 1 degreeincrements. However, the treatment couch 102 can be rotated at any otherdegree increments, such as, but not limited to, 1.5 or 2 degreeincrements.

In the illustrative embodiment, the gantry 112 is first positioned at 0degrees, then at between 30-60 degrees, then at between 300-330 degrees,respectively, prior to acquiring of the MV X-ray images. However, anyother gantry angle positions and/or combination of gantry angles arecontemplated. Therefore, the gantry may start at the 0 degree positionfollowed by the 300-330 degree position followed by the 30-60 degreeposition, or any other gantry angle combination. In alternativeembodiments, the gantry may be positioned only at two differentlocations. In yet other embodiments, the gantry may be positioned atmore than three different locations.

In an alternative embodiment, the initial gantry position is at 180degrees (i.e., radiation is pointing to the ceiling), then the gantry112 is rotated through 360 degrees by first positioning the gantry at180 degrees, then at between 210-220 degrees or between 185-240 degrees,then at between 140-160 degrees or between 120-175 degrees,respectively, prior to acquiring of the MV X-ray images. However, anyother gantry angle positions and/or combination of gantry angles arecontemplated.

Each of the MV X-ray images so generated includes the markers embeddedin the calibration phantom. In order to determine a position of thecalibration phantom from an X-ray image, first the positions of themarkers in the X-ray image is determined, then a one-to-onecorrespondence algorithm applied, whereby a correspondence is detectedbetween the projections of each marker in the X-ray image and themarkers themselves in the phantom. The positions of the markers in anX-ray image can be determined using a conversion algorithm by which theimage frame is converted to a binary image by thresholding. The binaryimage can then be analyzed by the controller 120 and the positions ofthe markers in the generated image determined. Other known techniquescould also be used to determine the positions of the markers in thegenerated X-ray image. Once the positions of the markers in the X-ayimage are determined, the controller 120 can form a one-to-onecorrespondence between the projections of each marker in the X-ray imageand the markers themselves in the phantom. This can be done bydetermining a possible orientation of the phantom that could produce thearrangement of the markers in the X-ray image. The possible orientationof the phantom translates into possible couch orientations/positionsthat would support such a phantom orientation. Various other availablealgorithms could be used for such determination. Once a match has beenfound, the estimated position of the calibration phantom is determinedto be the position of the calibration phantom at the corresponding couchrotation angle. By applying this image processing technique for all MVX-ray images obtained, the position of the phantom at each couchrotation angle can be determined. The MV X-ray images so generatedtherefore contain information about the positions of the calibrationphantom and corresponding treatment couch positions for all couchrotation angles.

The plurality of couch positions for all couch rotation angles obtainedin step S103 are next compared to corresponding reference couchpositions to determine the couch position offsets for each couchrotation angle. The reference couch position information can be obtainedin S104 using the digital readout system which is internal to theradiation treatment device (LINAC), or using an external readout system,which is external to the radiation treatment device, but it isintegrated with its operation.

When the internal digital readout system is used, the reference couchpositions are generated during the movement of the couch 102 asdescribed above in S103. During the movement of the treatment couch 102through the couch rotation angles, the position of the treatment couchfor each couch rotation angle is measured using the potentiometersand/or encoders integrated with the internal readout system. From this,the readout system can compute couch position information for each couchrotation angle. From this information, in S105, reference couch positioninformation (C_(rn)) (x′, y′, z′, θ′₁, θ′₂, θ′₃) for all couch rotationangles (θc_(n)) can be generated.

In an alternative embodiment, an external readout system can be used togenerate the plurality of reference couch locations. Such a system couldbe, but is not limited to, the ExacTrac™ (Brainlab Germany) or AlignRT™(VisionRT Ltd, London UK) imaging and control systems. These imaging andcontrol systems use real-time infrared (IR) and X-ray (ExacTrac™), orvisible light (AlignRT™) to measure the positions of the calibrationphantom (its surface), compare the measured positions with the detectedpositions, and determine position offsets between the two.

In operation, two (Brainlab) or three (VisionRT) camera systems, mountedfrom the ceiling of the treatment room (e.g., two room based X-rayImaging Chains), record the positions of IR reflective markers on thecalibration phantom surface, or the positions of the X-ray visiblemarkers on the phantom. From these images, the readout system cancompute 3D position information of the calibration phantom. When thecalibration phantom is moved to different locations by rotating thetreatment couch 102, one degree at the time, through its entire couchrotation range (i.e., during S103), the readout system can compute 3Dphantom position information for each couch rotation angle. From thisinformation, in S105, reference couch position information (C_(rn)) (x′,y′, z′, θ′₁, θ′₂, θ′₃) for all couch rotation angles (θc_(n)) can begenerated.

The readout systems (internal and external) also include imageregistration algorithms to compare, for each couch rotation angle(θc_(n)), the phantom/couch position information obtained using theX-ray image (S103) with a corresponding reference phantom/couch positioninformation obtained using the potentiometers and/or encoders (internalreadout system), or the IR or visible camera system (external readoutsystem). The difference between the determined (i.e., measured) (C_(mn))and reference (C_(rn)) couch positions for each couch rotation angle(Θc_(n)) can be calculated in S106. The calculated couch positionoffsets (couch position offset values Δ_(cn)) represent thelongitudinal, lateral, vertical, and rotational displacements,respectively, between the determined C_(mn) (x, y, z, θ₁, θ₂, θ₃) andthe reference (C_(rn)) (x′, y′, z′, θ′₁, θ′₂, θ′₃) couch positions forevery couch rotation angle (Θc_(n)),

where Δ_(cn)=(C_(mn))−(C_(rn)); Δ_(x)=x−x′; Δ_(y)=y−y′; Δ_(z)=z−z′;Δ_(θ1)=θ₁−θ′₁; Δ₂=θ₂−θ′₂, Δ_(θ3)=θ₃−θ′₃. These offset values Δ_(cn) canbe stored in a tabular format, as shown in Table 2 and saved in a memoryof the controller 120, for example.

TABLE 2 Couch Rotation Θc₀ Θc₁ Θc₂ Θc₃ Θc₄ . . . . . . Θc_(n) AngleΘc_(n) (degrees) Measured C_(m0) C_(m1) C_(m2) C_(m3) C_(m4) . . . . . .C_(mn) Couch location C_(mn) (x, y, z, θ₁, θ₂, θ₃) Reference C_(r0)C_(r1) C_(r2) C_(r3) C_(r4) . . . . . . C_(rn) Couch location C_(rn)(x′, y′, z′, θ′₁, θ′₂, θ′₃) Couch location Δ_(c0) Δ_(c1) Δ_(c2) Δ_(c3)Δ_(c4) . . . . . . Δ_(cn) offset Δ_(cn) (Δ_(x), Δ_(y), Δ_(z), Δ_(θ1),Δ_(θ2), Δ_(θ3))

In step S107, the calibration process S100 generates corrected targetposition (T′_(n)) information by combining the gantry-angle dependenttarget position information (Table 1) with the couch rotation dependentcouch offset information (Table 2), as shown in Table 3. Table 3 canalso be saved in a memory of the controller 120, for example.

By combining the information obtained from the gantry-angle dependentisocenter calibration process S101-S102 shown in Table 1, with the couchlocation offset information obtained from the couch angle-dependentcouch position offset calculation process S103-S106 shown in Table 2, anaccurate target position information (T′_(n)) for each gantryangle/couch angle combination can be obtained, as shown in Table 3. Theaccurate target position information (T′_(n)) represents the positionsof the target after the target has been repositioned from the originaltarget position (T_(n)) by an amount corresponding to the couch offsetvalues Δ_(cn) for respective gantry angles Θ_(gn) and couch rotationangles Θc_(n).

TABLE 3 Gantry Angle Θ_(g0) Θ_(g1) Θ_(g2) Θ_(g3) Θ_(g4) . . . . . .Θ_(gn) Θ_(gn) (degrees) Couch Rotation Θc₀ Θc₁ Θc₂ Θc₃ Θc₄ . . . . . .Θc_(n) Angle Θc_(n) (degrees) Couch location C₀ C₁ C₂ C₃ C₄ . . . . . .C_(n) C_(n) (x, y, z, θ₁, θ₂, θ₃) Couch location Δ_(c0) Δ_(c1) Δ_(c2)Δ_(c3) Δ_(c4) . . . . . . Δ_(cn) offset Δ_(cn) (Δ_(x), Δ_(y), Δ_(z),Δ_(θ1), Δ_(θ2), Δ_(θ3)) Accurate Target T′₀ T′₁ T′₂ T′₃ T′₄ . . . . . .T′_(n) position information T′_(n) relative to the isocenter

By combining the accurate isocenter calibration of the MV treatment beam(Table 1) and the couch compensation with the couch offset (Table 2),the treatment couch 102 and thus, the target, can be accuratelypositioned to the beam isocenter for every combination of couch 102rotation and gantry 112 rotation (Table 3). Various interpolationmethods, such as, but not limited to, linear interpolation, cubicinterpolation, Hermite interpolation, trilinear interpolation, linearregression, curve fit through arbitrary points, as well as nearestneighbour weighted interpolation methods can be used to obtainintermediate values for these parameters, including the couch locationoffset values Δ_(cn).

In alternative embodiments, process S100 can be repeated for differentcouch loads (i.e., different weights added to the treatment couch 102)to also calibrate for the load offsets. In such embodiments, for eachtreatment iteration, weights can be added to the treatment couch 102 tosimulate different sized patients, and the process steps S103-S104repeated to generate determined (i.e., measured) (C_(mn)) and referencecouch positions (C_(rn)). The difference between the determined (i.e.,measured) (C_(mn)) and reference (C_(rn)) couch positions for each couchrotation angle (Θc_(n)) can then be calculated in S106 by comparing themeasured and reference couch positions for each couch rotation angle andfor each load. The calculated couch position offsets (couch positionoffset values Δ′_(cn)) represent the longitudinal, lateral, vertical,and rotational displacements, respectively, between the determinedC_(mn) (x, y, z, θ₁, θ₂, θ₃) and the reference (C_(rn)) (x′, y′, z′,θ′₁, θ′₂, θ′₃) couch positions for every couch rotation angle (Θc_(n))and respective couch load;

where Δ′_(cn)=(C_(mn))−(C_(rn)); Δ′_(x)=x−x′; Δ′_(y)=y−y′; Δ′_(z)=z−z′;Δ′_(θ1)=θ₁−θ′₁; Δ′_(θ2)=θ₂−θ′₂; Δ′_(θ3)=θ₃−θ′₃. These offset valuesΔ′_(cn) can be stored in a tabular format, as shown in Table 4, andsaved in a memory of the controller 120, for example.

TABLE 4 Load (lbs/kg) L₀ L₁ L₂ L₃ L₄ . . . . . . L_(n) Couch locationΔ′_(c0) Δ′_(c1) Δ′_(c2) Δ′_(c3) Δ′_(c4) . . . . . . Δ′_(cn) offsetΔ′_(cn) (Δ′_(x,) Δ′_(y), Δ′_(z), Δ′_(θ1), Δ′_(θ2), Δ′_(θ3))

In yet other embodiments, additional offsets for collimator jaw, MLC,cones as well as applicator imperfections could also be included.

FIG. 4 illustrates a process S200 by which the treatment couch, andthus, a target, can be accurately positioned at the isocenter for eachgantry angle, because the couch imperfections introduced by the couchrotation relative to the isocenter have been compensated for as shownherein. In step S201, the isocenter is calibrated based on thecalibration offset information stored in Table 1. Once calibrated, thepositions of the target relative to the isocenter for each gantry anglecan be determined in S202. Then, in step S203, for each gantry angle,the determined target position can be corrected based on the couchrotation-angle dependent couch position offset information stored inTable 3. Additionally, target position can be further corrected byapplying the couch rotation-angle dependent couch position offsetinformation obtained for a particular weight of the patient as shown inTable 4, and thus correct for the sagging errors introduced by theweight of the patient.

FIG. 5 illustrates a process S300 by which, during radiation treatment,the target can be accurately and automatically positioned at theisocenter for each gantry angle based on the parameters saved in Tables1-3. As previously discussed, during treatment, a plurality of radiationbeams are directed to the target area of interest from several positionsoutside the body. The gantry is rotated to provide the radiation beamsfrom different positions. To aid the positioning of the patient, setupimages are acquired from multiple gantry angles and the target positionis determined from these images.

For each gantry angle, the images acquired during the radiationtreatment session (S301) are compared in S302 with previously determinedreference images of the target. When there is a difference between theacquired and reference images, it is determined that the target isoffset from the desired location. A target positioning offset is thusdetermined in S303 for each gantry angle. These offsets are corrected inS304 by an operator initiated automatic couch shift from the treatmentconsole room. In order to move the target to the correct location, foreach gantry angle Θ_(gn) where a target offset is determined, the targetis first moved (S305) to a first target location T_(n), which waspreviously determined to be the isocenter for that particular gantryangle Θ_(gn) (S301), as shown in Table 1. The target is moved to targetlocation T_(n) by moving the couch 102 to location C_(n), as shown inTable 3. In order to compensate for errors introduced by the couchmovement, the target is then automatically repositioned in S306 tolocation T′_(n), which represents the corrected target location. Thecorrected target location T′_(n) represents the location of the targetafter it has been moved from the initial target location T_(n) by anamount, which equals the couch rotation dependent offset value Δ_(cn)read from Table 3 corresponding to the rotation angle Θc_(n) associatedwith the couch location C_(n). The target location offsets are correctedin this way for every gantry angle where a target offset is detected.

Additionally, target position can be further corrected by applying thecouch rotation-angle dependent couch position offset informationobtained for a particular weight of the patient as shown in Table 4, andthus correct for the couch sagging errors introduced by the weight ofthe patient.

In yet another embodiment, the software program included in the softwaremodules of controller 120 can also include an optimization moduleoperable to optimize the treatment plan prior to and during treatmentdelivery. Optimization in real-time during treatment delivery can bettertake into account a variety of factors, such as patient anatomical andphysiological changes (e.g., respiration and other movement, etc.), andmachine configuration changes, including (e.g., beam output factors,couch error, collimator jaw and MLC imperfections and leaf errors,etc.). Real time modification of the beam intensity can account forthese changes by re-optimize beamlets in real time. The optimizationmodule can also account for cumulative errors and to adjust thetreatment plan accordingly. As such, the software can further includeoffsets for the errors introduced by collimator jaw and MLCimperfections.

It is thus apparent that an imaging-based quality assurance system andprotocol is disclosed for a radiation treatment device, comprising:performing an isocenter calibration process by using a target tocalculate deviations between a treatment beam axis and an imaging beamaxis at a plurality of gantry angles; for each gantry angle, determininga position of the target relative to the calibrated isocenter;generating couch rotation angle dependent couch position offsetinformation by: acquiring a plurality of X-ray images of a calibrationdevice positioned on the couch at different couch rotation angles;determining positions of the couch at all couch rotation angles based onthe X-ray images; comparing each determined couch position with areference couch position for each couch rotation angle; calculatingcouch position offsets between the determined and the reference couchpositions for each couch rotation angle; and calibrating the positioninformation of the target for each gantry angle using the couch rotationangle dependent couch position offset information.

It is further appreciated that the target position information can befurther calibrated using a couch compensation protocol to compensate forcouch load and position dependent mechanical deflections.

It is further to be appreciated that the system and method can furthercomprise determining offsets for collimator jaw or MLC imperfections,wherein the correcting of the target position includes correcting thetarget position by combining the gantry-angle dependent isocenter beamdeviation information with the couch rotation-angle dependent couchposition offset information, the load-dependent couch offset values, andthe offsets for collimator jaw or MLC imperfections.

It is also to be appreciated that a method for automatically positioninga target at an isocenter for each gantry angle is disclosed, comprising:generating images of the target at a plurality of gantry angles;determining a target position for each gantry angle from the acquiredimages; for each gantry angle, determining a target location offset bycomparing the acquired image for that gantry angle with a correspondingreference image; and correcting target location offset for each gantryangle by: moving the target to the isocenter; and correcting the targetlocation by moving the target by a distance which equals a previouslydetermined couch rotation dependent offset value. In embodiments, themethod can further comprise generating load-dependent couch offsetinformation by measuring errors included in the motion of the couch dueto different loads positioned thereon. The method can also furthercomprise correcting target position by combining the couchrotation-angle dependent couch position offset information with theload-dependent couch offset information.

It will be appreciated that the processes, systems, and sectionsdescribed above can be implemented in hardware, hardware programmed bysoftware, software instruction stored on a non-transitory computerreadable medium or a combination of the above. For example, a method forcan be implemented using a processor configured to execute a sequence ofprogrammed instructions stored on a non-transitory computer readablemedium. The processor can include, but not be limited to, a personalcomputer or workstation or other such computing system that includes aprocessor, microprocessor, microcontroller device, or is comprised ofcontrol logic including integrated circuits such as, for example, anApplication Specific Integrated Circuit (ASIC). The instructions can becompiled from source code instructions provided in accordance with aprogramming language such as Java, C++, C#.net or the like. Theinstructions can also comprise code and data objects provided inaccordance with, for example, the Visual Basic™ language, LabVIEW, oranother structured or object-oriented programming language. The sequenceof programmed instructions and data associated therewith can be storedin a non-transitory computer-readable medium such as a computer memoryor storage device which may be any suitable memory apparatus, such as,but not limited to read-only memory (ROM), programmable read-only memory(PROM), electrically erasable programmable read-only memory (EEPROM),random-access memory (RAM), flash memory, disk drive and the like.

Furthermore, the modules, processes, systems, and sections can beimplemented as a single processor or as a distributed processor.Further, it should be appreciated that the steps mentioned above may beperformed on a single or distributed processor (single and/ormulti-core). Also, the processes, modules, and sub-modules described inthe various figures of and for embodiments above may be distributedacross multiple computers or systems or may be co-located in a singleprocessor or system.

The modules, processors or systems described above can be implemented asa programmed general purpose computer, an electronic device programmedwith microcode, a hard-wired analog logic circuit, software stored on acomputer-readable medium or signal, an optical computing device, anetworked system of electronic and/or optical devices, a special purposecomputing device, an integrated circuit device, a semiconductor chip,and a software module or object stored on a computer-readable medium orsignal, for example.

Embodiments of the method and system (or their sub-components ormodules), may be implemented on a general-purpose computer, aspecial-purpose computer, a programmed microprocessor or microcontrollerand peripheral integrated circuit element, an ASIC or other integratedcircuit, a digital signal processor, a hardwired electronic or logiccircuit such as a discrete element circuit, a programmed logic circuitsuch as a programmable logic device (PLD), programmable logic array(PLA), field-programmable gate array (FPGA), programmable array logic(PAL) device, or the like. In general, any process capable ofimplementing the functions or steps described herein can be used toimplement embodiments of the method, system, or a computer programproduct (software program stored on a non-transitory computer readablemedium).

Furthermore, embodiments of the disclosed method, system, and computerprogram product may be readily implemented, fully or partially, insoftware using, for example, object or object-oriented softwaredevelopment environments that provide portable source code that can beused on a variety of computer platforms. Alternatively, embodiments ofthe disclosed method, system, and computer program product can beimplemented partially or fully in hardware using, for example, standardlogic circuits or a very-large-scale integration (VLSI) design. Otherhardware or software can be used to implement embodiments depending onthe speed and/or efficiency requirements of the systems, the particularfunction, and/or particular software or hardware system, microprocessor,or microcomputer being utilized.

Embodiments of the method, system, and computer program product can beimplemented in hardware and/or software using any known or laterdeveloped systems or structures, devices and/or software by those ofordinary skill in the applicable art from the function descriptionprovided herein and with a general basic knowledge of control systems,image processing and classification, and/or computer programming arts.

Moreover, embodiments of the disclosed method, system, and computerprogram product can be implemented in software executed on a programmedgeneral purpose computer, a special purpose computer, a microprocessor,or the like.

Features of the disclosed embodiments may be combined, rearranged,omitted, etc., within the scope of the invention to produce additionalembodiments. Furthermore, certain features may sometimes be used toadvantage without a corresponding use of other features.

It is thus apparent that there is provided in accordance with thepresent disclosure, an imaging-based calibration system and method forradiation treatment couch position compensations. Many alternatives,modifications, and variations are enabled by the present disclosure.While specific embodiments have been shown and described in detail toillustrate the application of the principles of the present invention,it will be understood that the invention may be embodied otherwisewithout departing from such principles. Accordingly, Applicants intendto embrace all such alternatives, modifications, equivalents, andvariations that are within the spirit and scope of the presentinvention.

1-52. (canceled)
 53. A method for automatically positioning a target atan isocenter for each gantry angle, comprising: generating images of thetarget at a plurality of gantry angles; determining a target positionfor each gantry angle from the acquired images; for each gantry angle,determining a target location offset by comparing the acquired image forthat gantry angle with a corresponding reference image; and correctingtarget location offset for each gantry angle by: moving the target tothe isocenter; and repositioning the target location by moving thetarget by a distance which equals a previously determined couch rotationdependent offset value.
 54. The method of claim 53, further comprisinggenerating load-dependent couch offset information by measuring errorsincluded in the motion of the couch due to different loads positionedthereon.
 55. The method of claim 54, further comprising correctingtarget position by combining the couch rotation-angle dependent couchposition offset information with the load-dependent couch offsetinformation.
 56. The method of claim 55, further comprising determiningoffsets for collimator jaw or MLC imperfections, wherein the correctingof the target position includes correcting the target position bycombining the couch rotation-angle dependent couch position offsetinformation, the load-dependent couch offset information, and theoffsets for collimator jaw or MLC imperfections.
 57. A method forcorrecting location of a target prior to irradiating the target with aradiation beam, comprising: positioning a target holding device at afirst location relative to a gantry; moving the gantry to a first gantryangle; moving the target holding device to a second location, the secondlocation corresponding to a location corrected for isocenter movementassociated with the movement of the gantry to the first gantry angle;and correcting the second location for isocenter movement associatedwith the movement of the target holding device to the second location.58. The method of claim 57, wherein the correcting of the targetlocation is automatic.
 59. The method of claim 57, wherein thecorrecting of the target location is automatic for a plurality of gantryangles.
 60. The method of claim 59, wherein isocenter movement valuesassociated with the movement of the gantry to the plurality of gantryangles are stored in a tabular format for later use.
 61. The method ofclaim 60, wherein isocenter movement values associated with the movementof the target holding device to the plurality of locations associatedwith the plurality of gantry angles are stored in a tabular format forlater use.
 62. The method of claim 61, wherein the correcting of thetarget location for a plurality of gantry angles and associated targetholding device movements is done automatically based on the previouslystored isocenter movement values.
 63. A method for irradiating a patientpositioned on a treatment couch with a radiation treatment beam from atreatment device including a gantry, comprising: positioning thetreatment couch at a first location; moving the gantry to a first gantryangle; moving the treatment couch to a second location, the secondlocation corresponding to a location corrected for isocenter movementassociated with the movement of the gantry to the first gantry angle;moving the treatment couch to a third location, the third locationassociated with a location corrected for isocenter movement associatedwith moving the treatment couch to the second location; and irradiatingthe patient.
 64. The method of claim 63, wherein the correcting of thepatient location is automatically done for a plurality of gantry anglesand associated treatment couch movements.
 65. The method of claim 64,wherein isocenter movement values associated with the movement of thegantry to the plurality of gantry angles are prerecorded values.
 66. Themethod of claim 65, wherein isocenter movement values associated withthe movement of the treatment couch to the plurality of locationsassociated with the plurality of gantry angles are prerecorded values.67. The method of claim 66, wherein the correcting of the targetlocation for the plurality of gantry angles is automatically done basedon the prerecorded isocenter movement values.
 68. A method forautomatically positioning a target at an isocenter for a plurality ofgantry angles, comprising: generating images of the target at aplurality of gantry angles; determining target positions forcorresponding gantry angles from the acquired images; for each gantryangle in the plurality of gantry angles: determining an isocenter offsetvalue by comparing the acquired image for that gantry angle with acorresponding reference image; determining isocenter location based onthe calculated isocenter offset value; and repositioning the target fromthe determined isocenter location by moving a couch holding the targetby a distance which equals a previously determined couch movementrelated offset value.
 69. The method of claim 68, wherein the couchmovement related offset value corresponds to a value by which theisocenter location is shifted when the target is repositioned.
 70. Themethod of claim 69, further comprising generating a target-dependentoffset value by measuring errors included in the movement of the couchdue to different targets positioned thereon.
 71. The method of claim 70,further comprising correcting target position by combining the couchmovement related offset value with the target-dependent offset value.72. The method of claim 71, further comprising determining offset valuesfor collimator jaw or MLC imperfections, wherein the correcting of thetarget position includes correcting the target position by combining thecouch movement related offset values, the target-dependent offset value,and the offset values for collimator jaw or MLC imperfections.